Bonding modes of species chemisorbed on tungsten single crystal faces
Thesis The relative bonding energies of hydrogen, nitrogen, and oxygen at three symmetric sites and W(100) surfaces were obtained by means of the Extended Hueckel Molecular Orbital Theory. The W(100) surface was represented by finite arrays of tungsten atoms (W/sub n/). The energy change for the reaction W/sub n/ + X -- W/sub n/X(X-- H, N, O) was calculated for various assumed configurations of the W/sub n/''molecules''. The preferred site for a hydrogen adatom was found to be the single coordination number (1 CN) site or the site above a surface tungsten atom. The nitrogen adatom preferred the five coordination number (5 CN site) or the four-fold site with a tungsten atom below and four tungsten atoms surrounding the nitrogen atom. The oxygen adatom preferred a two coordination number (2 CN) site or a two-fold, bridging site between two surface atoms. A model for the dissociative adsorption of CO on W(100, 110, 111) surfaces at room temperature was proposed based on flash desorption spectrometry results from mixed adsorption of C/sup 16/O and /sup 18/O/ sub 2/ on the above surfaces. The isotopic mixing of the oxygen in the desorbed CO molecules is indicative of dissociative adsorption. Results also contradicted the hypothesis that associatively adsorbed CO was converted to the dissociatively adsorbed C and O adatoms by the heating of the surfaces. The limiting ratios of C/sup 18/O: CO/sub total/ desorbed from low and high coverages of preadsorbed C/ sup 16/O followed by saturated co-adsorbed /sup 18/O/sub 2/ coverages on the above tungsten surfaces enabled bonding models to be developed for the dissociated C/sup 16/O co-adsorbed on the surface with associatively adsorbed is / sup 18/O/sub 2/. (34 figures) (auth)
- Research Organization:
- Ames Lab., Ames, IA (United States)
- DOE Contract Number:
- W-7405-ENG-82
- NSA Number:
- NSA-29-010646
- OSTI ID:
- 4401449
- Report Number(s):
- IS-T-608
- Resource Relation:
- Other Information: Thesis. Orig. Receipt Date: 30-JUN-74
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
Ceramics
& Other Materials-Metals & Alloys-Corrosion & Erosion & Surface Phenomena
*CARBON MONOXIDE- BINDING ENERGY
*HYDROGEN- BINDING ENERGY
*NITROGEN- BINDING ENERGY
*OXYGEN- BINDING ENERGY
*TUNGSTEN- CHEMISORPTION
DESORPTION
MOLECULAR ORBITAL METHOD
MONOCRYSTALS
SURFACES